1. Field of the Invention
The invention relates to countercurrent chromatography systems, and more particularly to an improved column design for use in countercurrent chromatography.
2. Description of the Related Art
Chromatography is a separation process that is achieved by distributing the substances to be separated between a mobile phase and a stationary phase. Those substances distributed preferentially in the moving phase pass through the chromatographic system faster than those that are distributed preferentially in the stationary phase. As a consequence, the substances are eluted from the column in inverse order of their distribution coefficients with respect to the stationary phase.
Chromatography is widely used for the separation, identification, and determination of the chemical components in complex mixture. Chromatographic separation can be utilized to separate gases, volatile substances, nonvolatile material, and polymeric material including biological substances.
The performance of countercurrent chromatography systems depends largely on the amount of stationary phase retained in the column, which determines both the resolving power of the solute peaks and the sample loading capacity. Numerous countercurrent chromatography systems have been developed to optimize the retention of the stationary phase of a sample in the column. The maximum attainable retention level tends to fall sharply with the application of higher flow rates of the mobile phase, resulting in loss of peak resolution. Consequently, the applicable flow rate has become one of the major limiting factors in countercurrent chromatography.
Some countercurrent chromatography systems utilize a complex hydrodynamic motion in two solvent phases within a column comprising a rotating coiled tube. If, for example, a horizontally mounted coil is filled with water and is rotated around its own axis, any object, either heavier or lighter than the water present in the column will tend to move toward one end of the coil. This end is then called the “head” and the other end, the “tail” of the coil. When the coil is filled with two immiscible solvent phases, the rotation establishes a hydrodynamic equilibrium between the two solvent phases, where the two phases are distributed in each turn at a given volume ratio (equilibrium volume ratio) and any excess of either phase remains at the tail of the coil.
When one of the solvent phases is added to the coil at its tail end and is further eluted from the coil at its head end, the hydrodynamic equilibrium tends to maintain the original equilibrium volume ratio of the two phases in the coil and thereby a certain volume of the other phase is permanently retained in the coil while the two phases are undergoing vigorous agitation with rotation of the coil. As a result, the sample solutes present in one phase and introduced locally at the inlet of the coil are subjected to an efficient partition process between the two phases and are chromatographically separated according to their partition coefficients.
In some cases, countercurrent chromatography utilizes a multi-layer coil as a separation column to produce a high efficiency separation with relatively favorable retention of the stationary phase in many solvent systems. Thus, countercurrent chromatography has been employed to achieve efficient extraction of a sample solution under relatively high flow rates. Previous column designs have relied on the use of a helical coil of tubing. U.S. Pat. No. 4,430,216, hereby incorporated by reference in its entirety, describes a preparative countercurrent chromatography utilizing a multiple layer coiled column. The coiled column design includes a length of plastic tubing wound around a coil holder to form multiple layers of the coil. Although this system works reasonably well for some solvents, these systems often fail to retain a satisfactory amount of the stationary phase for highly viscous, low interfacial solvent systems such as polymer phase systems, which are useful for the separation of macromolecules and particulates. In addition, the coiled tubing configuration is difficult to assemble, and connecting the ends of neighboring spiral tubing is rather difficult.